Magnetogenerator



a "w a N R I;

Q I Q Tit. 18, 1938. w. cox 2,183

MAGNETOGENERATOR Filed Feb. 10, 1936 2 Sheets-Sheet l INVENTOR. lRV/N WCOX ag-Z ATTORNEY.

I. W. COX

MAGNETOGENERATOR Oct. 18, 1938.

Filed Feb. 10, 1956 2 Sheets-Sheet 2 x 0 9 v m c w a 4 m w. w v Q n! H w1 W W m m 2 WI QM. O/n S a R R mm ww a a m. QN

Patented Oct. 18, 1938 UNITED STATES PATENT OFFICE 2,133,686MAGNETOGENEBATOR Irvin W. Cox, Chicago, Ill., assignor to AssociatedElectric Laboratories, Inc., Chicago, 111., a corporation of DelawareApplication February 10, 1936, Serial No. 63,113

3 Claims.

having a more efficient magnetic circuit and a more efficient mechanicalconstruction, whereby a generator of a given power output may be moreeconomically produced and a greater power output may be obtained from agiven weight or cost of material.

Additional objects are to devise a method for preventing undue selfcoercion of the permanent magnets following magnetization, and a. methodfor reliably performing an artificial ageing operation of the generatorbefore test which brings the performance capacity of the generator downto a value corresponding to that obtained after severe service.

General description Pursuant to a realization of the main object of theinvention, a novel structure has been produced, the design of which isbased particularly on'the efllcient use of permanent-magnet materialhaving a very high optimum value of sustained specific magneto-motiveforce, lying above the maximum specific magneto-motive force of the bestknown cobaltsteel permanent-magnet material, and capable of sustaining ahigher maximum field energy per unit volume of permanent-magnet materialthan the best known cobalt-steel permanent-magnet material.

The permanent-magnet material used in the improved magneto-generatorconstruction is a ferrous alloy containing in the neighborhood oftwenty-five per cent nickel, twelve to fifteen per cent aluminum, two tofour per cent cobalt, and the remainder iron. This material is firstcast to the desired sizeand configuration and is then allowed to cool,following which it is reheated in the performance of a process known asprecipitation hardening. It is understood that this hardening operationpermits particles to crystallize out of solution, whereby the resultingaggregate material becomes magnetically very hard, acquiring a veryhighcoercivity and a relatively low permeability.

Tests of cast and treated samples of this mate rial show a residualflux, following saturation, of

seven thousand maxwells per square centimeter of cross section at zeroexternal magnetmmotive force, and that a coercing magneto-motive forceof 430 gilberts per lineal centimeter is required to reduce this flux tozero. These figures compare with ten thousand maxwelis and 250 gilbertsfor the best obtainable grades (about thirty-six per cent cobalt) ofcobalt steel.

Comparative tests show further that the optimum working point of theiron-aluminum-nickelcobalt material is with a magneto-motive force ofabout 310 gilberts developed in the external field per linear centimeterof magnet material, which is in excess of the total coercive force (250gilberts) per centimeter required to reduce the fiux through the bestcobalt steel to zero. With this developed magneto-motive force (310gilberts per centimeter), the flux density in the cast material is 4500maxwells per square centimeter of cross section, while at the optimumvalue of magneto-motive force (160 gilberts per centimeter) the fiuxdensity in the tested cobalt steel is slightly in excess of seventhousand maxwells per square centimeter. Multiplying the maxwellsobtaining at the optimum value of developed gilberts, we obtain anoptimum field-energy product of 4500x310=1,395,000 gilbert-maxwells percubic centimeter of the cast material. This is substantially in excessof the corresponding fieldenergy product (1,152,000 gilbert-maxwells percubic centimeter) of cobalt steel. From these figures, it will be atonce apparent that for a given external field structure to be energized,a welldesigned cast magnet of the described material, while of asomewhat lesser cubical content than an equivalent magnet of cobaltsteel, is much shorter, measured between its pole faces, than the one ofcobalt steel. It was the recognition of this fact that enabled the noveldesign hereinafter disclosed to be evolved.

It will be understood, of course, that a large saving in cost isrealized by the use of the cast material, not alone from the fact thatless labor is required in casting it into form than in working steel,but also because of the relatively high cost of cobalt, of which thecast material contains only a small amount as compared to aboutthirtysix per cent for what is known as cobalt steel.

It will be understood further that other alloys than the one describedmay be used, providedthey respond to precipitation hardening or otherprocesses to acquire a high coercivity and a high energy-product value,as above set forth.

Readily distinguishable features of the novel construction disclosedherein may be enumerated as follows:

1. By employing magnetic material of high coercive force, relativelyshort magnets may be used which may be made of rather largecross-section and still be comparatively small in volume,

whereby relatively 'small magnets may give .the required power in themagnetic field.

2. Two parallel magnetic circuit paths are employed to supplymagneto-motive force to the useful field of the structure. The permanentmagnets are located on opposite sides of the useful field of thegenerator, whereby a more symmetrical device is obtained. Thisarrangement permits a more uniform distribution of magnetic flux in thepole shoes and results in a lower apparent reluctance of the pole shoesthan that which would obtain if the permanentrmagnet material were allconcentrated on one side of the structure, in which latter case ahigher-.magnetomotive force would need to be employed, which wouldnecessitate increasedlength and weight of magnet material.

3. With the improved construction, the armature chamber is effectivelyenclosed on all sides by the essential parts of the structure, wherebyno additional protective, enclosing members or sheets are required: .theusual bearing end plates enclose the ends of the inter-pole space; themagnets themselves enclose the front and rear sides; and the pole shoesenclose the top" and bottom of thearmature chamber.

4. The magnets are cast to the desired size and shape, requiring onlythat the pole faces of the magnets which contact the pole shoes of thegenerator be ground smooth to insure a good metal-to-metal contact,while additionally the magnets are cast with open slots through whichthe magnet-mounting screws may pass, as the extreme hardness of thematerial practically precludes drilling.

5. By virtue of the short-magnet construction, utilizing magnets whichdo not extend beyond the surface of the pole pieces of the generator,the magnets may be readily magnetized to saturation after the magneticstructure has been completely assembled, and the magnetization may beperformed in such a way as to produce the poles of the permanent magnetsat the desired points (adjacent the pole shoes of the structure), forthe pole shoes of the generator are left uncovered by the magnetsthemselves, making it easy to apply the pole pieces of a magnetizer tothe pole shoes of the generator for the purpose of magnetizing thepermanent magnets in place in the assembled structure.

6. The efficiency of the magnetic path through the armature has beenincreased by recessing or grooving the armature end plates so as topermit of a greater effective length 'of armature pole within a givenlength of armature chamber.

7. In addition to the foregoing, incidental benei'lts resulting from theimproved construction have to do with such features as permitting moreready access to the crank shaft and the set screw which holds it inplace, whereby the crankshaft assembly may be more readily removed forrepair or replacement, and it permits also of a more advantageouslocation of an oil hole for the oiling of the distant bearing of thecrank shaft.

. Detailed description Referring now to the accompanying drawings,comprising Figures 1 to 8, Figures 1 to 7 show The structure Referringnow particularly to Figures 1 to '7: Figure 1 is a front view of the newmagnetogenerator; Figure 2 is a view as seen from the top; Figure 3 isan end view as seen from the left; Figure 4 is an end view of thegenerator as seen from the right; Figure 5 is a front sectional viewtaken along the line 5-5, Figure 2; Figure 6 is a top sectional viewtaken along the line 6-6, Figure 1; and Figure 7 is a left section takenalong the line 1-1, Figure 1.

The magnets l and 2, whose cross-section may be seen best in Figure 7,are substantially U- shaped in cross-section. In the model illustrated,the magnets have relatively short horizontal limbs, but the length oflimb may be greater when additional magneto-motive force is required.Each of these magnets is pre-cast to the desired size and shape and ismachine ground only on its pole faces where it contacts with the polepieces 8 and 4., which latter are preferably made of cold-rolled steel.Mounting screws El to 53, best seen in Figure 7, pass thru open slotsthe end of the pole pieces 3 and 4, as may be seen best in Figures 5 and6. The end plates are machined so as to leave an integral disc on. theinside surface thereofconcentric with the armature shaft, which servesto fix the distance between the poles, while upward extensions of theend plates hold the bearings for the crank shaft.

The armature 9, as-is' shown in Figures 5, 6, and 'I, is of the usualshuttle type of construction, giving ample space for the armaturewinding. The armature is provided with end plates I ii and H into whichthe armature shaft-members' l2 and I3 are placed and are secured by anoperation known as staking. It is to be noted that the allowableeffective length of armature pole is increased by machining away part ofeach end plate around the rim, thereby decreasing the armaturereluctance. The shaft bearings l4 and iii are staked into the end platesI and 8, and they are proportioned so as to space the armature assemblyaccurately within the armature chamber and hold it against substantialendwise movement.

Bearings l6 and I! for the crank shaft l8 and the sleeve 23, formedintegrally with the drivin gear 22, are staked in the end plates 1 and8. The crank-shaft stop-collar l9, threaded on the inside, is screwedonto the end of the crank shaft l8 to limit the endwise movement ofcrank shaft [8 imparted by the interaction between the cam collar 20(see Figures 1 and 2) and the cam cut in the sleeve 23 forming anextension of driving wheel 22. Cam collar 20 is held in position by pin'2|, Figures 1 and 5. This endwise movement of crank shaft l8, it will beunderstood, takes place when the crank 30 is turned by the handle 3|, inorder to shift the spring combination by the-means of the thrust actionof buffer 33, composed of insulating material and fitted snugly in ahole in the end of the crank shaft it. The coiled spring 28 restores thecrank shaft 18 endwise to the position shown in the drawings when thecrank is released. The assembly composed of the crank shaft and theBearings I6 and I! may be oiled through oil holes 51 and 56, andbearings l4 and I! may be oiledthrough holes 55 and 66. It is to benoted particularly that oil hole 51 is conveniently located on theextended insidev portion of bearing l6. It is accessible for oiling inthis position in the illustrated construction because the magnetstructure "has been changed from the usual horseshoe form; in the usualgenerator construction, an oil hole placed on the inside portion of thisbearing is inaccessible because it. is covered by the horseshoepermanentmagnets.

Armature pinion 26, seen best in Figures 1, 4, and 5, is fitted over theend of shaft member ll and is secured in place by pin 21.

. In order to fit'th'e generator better for use in a portable container,the crank handle 2| is of the folding construction illustrated, coiledspring '32, Figure 2,being provided to restore the crank handle 3| tothe position shown after it has been extended in use, perpendicular to.crank 36.

Although the armature II has been shown unwound for the sake ofsimplicity, it will be understood that in practice the armature is woundwith the desired size of wire until the winding space is filled to suchan extent that a cross-section of the wound armature is substantiallycircular.

One end of the armature winding is soldered to lug 46, secured to thefront armature-endplate ii, as may be seen in Figures 5, 6, and 7.

The other end of the armature winding is secured to lug 36, which isheld beneath the nut 39 which holds the contact stud 34 in place. Thecontactstud assembly is insulated from the metallic frame structure ofthe armature by bushing 35 (Figures 5 and 6), washer 36,'and plate31,-all composed of insulating material.

As seen in Figures 1 to 3, a spring assembly, mounted on bracket 40, issecured to the rear end plate 1 by screws 4|, Figures 2 and 3. Of themembers in the spring assembly mounted on bracket 40, by means of screws42, and suitably insulated from each other, the terminal plate 44 is incontact with the spring washers held under the heads of .screws 42, andthrough the screws 42 with the 'frame structure of the generator,whereby plate 44 may conveniently serve as one terminal point to whichan output conductor may be secured by means of the illustrated bindingpost, or terminal screw. Contact with the other terminal of the armaturewinding is maintained by contact spring 45, which presses against screw,to which the other output lead of the generator may be connected. Theremaining terminal plate in the spring assembly is connected to thecontact spring 41, normally engaged by the traveling spring 48 forwhatever switching function may be necessary in the use of thegenerator;

Maghetizing the assembled generator Referring now particularly to Figure8, the generator of Figures 1 to 7 is shown in association with amagnetizer before the crank assembly has been placed in the generator,but after the generator is otherwise structurally complete. Bracket 46and associated spring asembly may be mounted either before or after themagnetization of the permanent magnets has been accomplished.

- The magnetizer consists essentially of spooltype electromagnets 6i and62, provided with circular cores 63 and 64 and a return yoke 65,connecting the lower ends of the cores together, forming a horseshoeelectro-magnet. Pole nieces 66 and 61 are provided. Pole piece 61 issecured in position by bolts 12 and I3 threaded into tapped holes inthe'end of core 64, while pole-piece 66 is slidably secured to core 63of spool 6| by bolts I0 and II.

The pole pieces 66 and 61 are formed so' that the ends thereof are ofsubstantially the same wid h as the pole shoes 6 and 4 of the generator,and are moreover preferably of the same thickness as the spacing betweenthe assembled permanent magnets, whereby contact between pole pieces 66and 6'| of the magnetizer and pole shoes 4 and 3 of the generator ismade substantially over the entire exposed surface of the pole shoes ofthe generator. In preparation for the magnetizing operation, the polepiece 66 may be slid to the left in order to permit the generator to beplaced in the illustrated relationship to pole piece 61, with the innerparts of the bearing inserts l6 and i1 lying within slots 14 and 15,milled in the edges of the pole piece 61. The pole piece 66 may then bebrought up tightly into engagement with pole piece 4 of the generator,following which bolts 10 and H may be tightened, if desired, to hold thegenerator in place until magnetization is effected. It will beunderstood. of course, that current is preferably applied to thewindings of the magnetizer only after the gen-,

erator has been placed into position to avoid unnecessary waste ofenergy and accompanying heating of the coils of the magnetizer, as wellas to facilitate the handling of the parts, which can be accomplishedmuch better when the magnetizer is not energized.

After the current has been permitted to flow a desired length of timethrough the magnetizer, whereby a saturated condition is produced in themagnets l and 2, the current may be turned oil, and the generatorremoved from the magnetizer.

A great advantage lies in magnetizing the permanent magnets in place,for then the magnets are at no time after being magnetized subjected tothe high reluctance of an all-air flux path as they would be, ofnecessity, if they were mounted after having been magnetized. It hasbeen observed that the magnets are deteriorated as much as twenty percent if removed from the structure and replaced, resulting from what maybe termed self-coercion.

Inthe event that the reluctance of the poleshoe-armature magnetic path(in shunt of the magnets during magnetization) draws sufficient flux torender it difficult to impress the desired magneto-motive force with agiven magnetizer, the reluctance of this shunt path during magnetizationmay be reduced by turning the armature ninety degrees.

Artificial ageing and testing After a generator has been completed, itmust be tested to insure that its performance in service will be atleast equalto a predetermined standard. It has been found that agenerator of the'disclosed construction falls of! somewhat and thatabout the most severe demagnetizing condition imposed upon it in serviceis cranking it when it is connected to a load circuit of negligibleresistance. The heavy current then flowing causes the revolving armatureto present an abnormally high inter-pole-shoe reluctance during part ofeach half-cycle, causing the magnets to undergo self-coercion.Therefore, since any generator is likely at some time to be operatedunder short-circuit conditions, each generator, before the output testof it is made, is operated long enough (say ten seconds) atshort-circuit load to ensure that its deterioration (about ten per centof initial performance) has substantially reached its maximum. Thegenerator is thereby artificially aged, and no further substantialreduction in its output capacity may be expected to result eitherfromthe mere lapse of a reasonable period of time or from operation undersevere load conditions. After the described pre-deterioration andconsequent ageing operation has been accomplished, a test or the outputcapacity of the generator may be relied upon to indicate the expectedperformance of the generator in actual service over a long period oftime.

Additional information Although, for the sake of simplicity, a bottomview of the generator has not been shown, it may be-pointed out thatmounting holes (four of them) are drilled and tapped in the lower poleshoe 1 of the generator.

Additionally, the density of the cast magnet material is'only about ninetenths that of a magnet material, s'uch as cobalt steel. Therefore,since the magnets are smaller than equivalent cobalt-steel magnets,as-previously explained, a

2,188,686 in performance after it has aged for some time,

substantial reduction in weight accrues from using the disclosedmagnets.

What is claimed is:

1. The method of producing a magneto generator which has an armature, apair of pole shoes, and a permanent magnet for energizing the poleshoes, which consists in first assembling the parts enumerated intotheir permanent locations, and in then applying sumcient magnetomotiveforce directly across the pole-shoe-armature path to substantiallysaturate the permanent magnet in a circuit path parallel to thepole-shoe-armature path.

2. The method of producing a magneto generator the characteristics ofwhich do not deteriorate appreciably responsive either to the passage ofa substantial period or time or responsive to severe. service operation,which consists in applying asufiicient magneto-motive force to the fieldstructure after assembly to produce permanent-magnet saturation, and inthen operating the generator for an appreciable time under short-circuitconditions. l

3. The method of magnetizing the permanent magnets of a generatorcomprising a shuttle armature enclosed by a field structure comprisingtwo pole pieces joined at their ends by two permanent magnets, whichconsists in inserting the assembled field structure and armature betweenthe poles of an electromagnet with the two generator pole pieces inengagement with the two poles of the magnet, respectively, and incausing the electromagnet to drive a saturating flux through a magneticcircuit which includes the two permanent magnets and the armature inparallel.

I IRVIN W. COX.

